Navigating our environment is a critical behavior that requires proper perception of self-motion (heading). Given the importance of heading, many cortical areas must be involved. Elucidation of the full cortical network will require a systematic evaluation of candidate cortical areas like V6. In this grant, I propose a thorough characterization of V6 neuronal activity in response to various heading signals. In Aim 1, I will record from V6 neurons to determine responses to optic flow (visual), platform motion in the dark (vestibular), and the coherent combination (visual+vestibular) of the two heading signals. I will use the same stimuli that have been valuable in evaluating neurons in other cortical areas that process heading signals, such as the dorsal medial superior temporal area (MSTd) and the ventral intraparietal area (VIP), allowing valuable direct comparisons to be made. In Aim 2, I will test whether the tuning of V6 neurons' reference frames remain invariant to changes in eye-position for visual, vestibular, and congruent combination of the visual and vestibular heading cues. Reference frames help us understand how behavior is coordinated among different sensory modalities. Intuitively, since we perceive heading relative to a head/body frame of reference, it is reasonable to assume that sensory heading signals will be transformed to a head/body reference frame. However, in both MSTd and VIP, visual heading signals are eye-centered making explicit testing for heading reference frames necessary. In Aim 3, I will test the potential of V6 to utilize motion parallax as a heading cue. Direction-dependent disparity tuned (DDD) MSTd neurons have already been implicated to use motion parallax as a heading cue. However, the vergence angle was never varied when DDD neurons were previously assessed. Because DDD neurons were evaluated at a single fixation distance, it is uncertain if the tuning profiles of DDD cells relate to absolute distance or absolute disparity. The latter is required for the tuning profiles of DDD neurons to be invariant with viewing distance (vergence angle). Overall we are interested in understanding the full network of cortical areas involved in heading. Accomplishing this goal requires systematic evaluation of candidate cortical areas such as V6. Because heading perception is inherently a multi-sensory problem, understanding this system will invariably produce insights into impairments where multi-sensory integration is a primary deficit, such as vertigo.